Blood compatible microencapsulated detoxicants and method for making

ABSTRACT

Blood compatible microencapsulated detoxicants suitable for the detoxification of blood in an extracorporeal shunt are made by coating a solid detoxicant with a semipermeable polymer membrane and then coating the membrane with a non-interfering layer of a blood compatible protein.

United States Patent [191 Chang [54] BLOOD COMPATIBLE MIC ROENCAPSULATEDDETOXICANTS AND METHOD FOR MAKING [75] Inventor: Thomas M. S. Chang,Montreal,

Quebec, Canada [73] Assignee: Research Corporation, New York,

[22] Filed: Dec. 17, 1970 [21] App1.No.: 99,269

[52] US. Cl. ..l17/82, 23/2585, 117/81, 117/100 B, 117/100 C, 117/165,424/9, 424/10, 424/35, 424/36, 424/101, 424/125,

424/183 [51] Int. Cl. ..A6lk 23/02, G01n 31/06 [58] Field ofSearch..424/36, 35,125; 117/81,

l17/DIG.11,82,100B

[11] 3,725,113 1 Apr. 3, 1973 [56] References Cited UNITED STATESPATENTS 3,522,346 7/1970 Chang ..424/3S OTHER PUBLICATIONS Chang,T.M.S.: Canadian Journal of Physiol. and PharinacoL, Vol. 47, Pages1,043-1,045 (1969). Chang, T.M.S. 'et aL: Trans. Amer. Soc. Artif.Organs, Vol. 16, Pages 141-148 (1970).

Primary Examiner-Ralph I-Iusack Attorney-Stowell & Stowell [57] ABSTRACT4 Claims, No Drawings BLOOD COMPATIBLE MICROENCAPSULATED DETOXICANTS ANDMETHOD FOR MAKING This invention relates to microencapsulateddetoxicants intended for use in the extracorporeal detoxification ofblood.

The first artificial kidney in clinical use operated as extracorporealhemodialyzers. Permeant metabolites from the blood being detoxifieddiffused through a semipermeable membrane at a rate proportional to thesurface area of the membrane but inversely proportional to itsthickness. Much effort has gone into the design and development ofsimpler, more compact and less costly hemodialysis systems.

Using another approach, T.M.S. Chang, Trans. Amer. Soc. Artif. Int.Organs, 12, 13 (1966) demonstrated the feasibility of utilizingsemipermeable microcapsules as artificial kidneys. It was suggested thata compact device could be made by packing semipermeable microcapsulesinto an extracorporeal shunt through which blood could be perfused.Because of their lesser membrane thickness and relatively larger totalsurface area as compared to a dialysis membrane, microcapsules couldform the basis of a more efficient artificial kidney.

A number of solid absorbents, such as charcoal and ion exchange orchelating resins, can remove waste metabolites, toxins and otherundesirable materials from perfusing blood. Activated charcoal inparticular is very effective in absorbing many uremic waste metabolitesand exogenous toxins. However, charcoal granules in direct contact withblood adversely affect the formed elements present in blood and releasefree particles into the circulating blood capable of causing emboli incertain major bodily organs.

Chang et al, Can. J. Physiol. PharmacoL, 44,1 15-128 (1966) and Trans.Amer. Soc. Artif. Int. Organs, 14, 163-168 (1968), reported thatembolism-causing particles can be avoided and destruction of formedelements lessened by providing the absorbent as. an aqueous slurry insemipermeable microcapsules. The encapsulated absorbent does not come indirect contact with the formed elements of perfusing blood and freeparticles of absorbent are retained within the microcapsules. Permeantwaste metabolites and toxins diffuse through the semipermeable membranewalls defining the microcapsules to be absorbed by the detoxicant andremoved from the diffusing blood.

The semipermeable microcapsules described in Chang et al above resembleartificial cells. The cell wall membranes in these microcapsules areflexible and there is a tendency for the microcapsules to close packincreasing their resistance to blood perfusion and occasionally rupturewhen used in large quantities.

More recently, US. Pat. No. 3, 522,346 to Chang describes semipermeablemicrocapsules made by the direct coating of polymer, together with aheparinquaternary ammonium complex onto granules of solid detoxicant.The resultant microcapsules are somewhat non-uniform in configuration,generally conforming in shape to that of the granules coated, and resistclose packing when used in large quantities; the membrane is lessflexible and there is less of a tendency to rupture under stress. Thepresence of heparin in the membranes renders the microcapsulesnonthrombogenic.

l have now discovered improved double coated detoxicant microcapsuleseven more efficient when used in the extracorporeal detoxification ofblood. My novel microcapsules arecharacterized by having thesemipermeable membrane directly coated onto the solid detoxicantfollowed by a second coating of a blood compatible protein. The outerprotein layer substantially avoids any adverse effect on the formedelements present in blood without imparing the efficiency of themicrocapsules as blood detoxicants.

More specifically, the present invention is a microencapsulateddetoxicant composition adapted for reaction in an extracorporeal shuntwith waste metabolites and toxins found in blood comprising a soliddetoxicant coated first with a semipermeable polymer membrane having aneffective pore size permitting waste metabolites and toxins to diffusetherethrough and second with a permeable outer layer of a bloodcompatible protein.

The detoxicants contemplated for use in practicing my invention arethose solids useful in the removal of waste metabolites and toxins fromcirculating blood. Various absorbents including ion exchange resins havebeen used for this purpose; Charcoal, particularly activated charcoalofvegetable origin, is of most general application.

The precise constituents or chemical nature of the polymer utilized tocoat the absorbent is not critical. However, the polymer should becapable of being formed into a semipermeable membrane about the granulesof absorbent with an effective pore size permitting molecules of wastemetabolite to diffuse therethrough to contact the absorbent.'lt is alsoapparent that the polymer selected be insoluble in water, capable ofsterilization, stable to blood and non-toxic. While the presentinvention is described with particular reference to collodion, otherhydrophilic polymers, particularly cellulosic polymers such as celluloseacetate, cuprophane, 'cadophane and the like, may be utilized.

The granules of absorbent are most conveniently coated by stirring witha solution of the desired polymer in a voltatile organic solvent. Thesuspension is slowly stirred until most of the solvent evaporates andthe still-wet coated granules spread out and dried under moderateheating. The dried coated granules are repeatedly washed with largevolumes of sterile water until free of uncoated absorbent granules andother smaller particles.

The polymer coated microcapsules are generally sterilized prior to finalcoating with protein asby autoclaving at 121C and 15 psi. (The absorbentis preferably p'resterilized prior to coating with polymer). Thesterilized microcapsules are then coated with a bloodcompatible protein,such as albumin or collagen, preferably from sterile aqueous solution. Arelatively thin permeable layer of protein is deposited which does notinterfere with diffusion through the semipermeable polymer membrane.

The detoxicant microcapsules according to the present invention arenon-uniform generally conforming to the shape of the absorbent granulescoated. While not round, they approximate spheres about 1 mm indiameter. Membrane thickness is in the range of -1 ,000 A and effectivepore size in the range 5-45 EXAMPLE 1 Preparation of microcapsules Threehundred grams of 6-14 mesh activated coconut-derived charcoal granuleswas wrapped in a sterile cloth, autoclaved at 121C and 15 psi for onehour and allowed to stand in the sealed wrapping for at least 1 day. Thecharcoal was then placed in a beaker and a solution containing 15 ml ofU.S.P. collodion in 300 ml of ether and 15 ml of ethanol was added withstirring. When most of the solvent had evaporated, the slightly wetpolymer-coated charcoal was spread out in a large tray and dried forhours at 50C in a ventilated oven. The dried microcapsules were sieved(40 mesh) with bacteria-free distilled water until free of fineparticles.

The washed microcapsules were then placed in a shunt of the typedescribed in Example 3, primed with bacteria-free water and autoclavedfor 30 minutes at 121C and 15 psi. After cooling, the priming water wasremoved and a sterilized saline solution containing 1 percent humanalbumin added; the shunt containing the microcapsules and albuminsolution was kept sealed for 15 hours at 4C. The albumin solution isdisplaced with sterile saline under sterile technique just prior to use,generally within 24 hours.

' EXAMPLE 2 In vitro tests The following batch experiments were effectedat 37C using double coated microencapsulated charcoal prepared asdescribed above.

A. One gram of microcapsules was stirred with 30 ml of a solutioncontaining 21 mg percent of creatinine. The creatinine concentrationdropped at a rapid rate; 50 percent was removed within 12 minutes.

B. Thirty grams of microcapsules was stirred with 9 l of a solutioncontaining 1 1 mg percent of uric acid; 50 percent of the uric acidpresent was removed within 18 minutes.

C. In a single pass experiment, a solution containing 20 mg percent ofcreatinine was passed through 300 g of microcapsules. The creatinineclearance rate was 150 ml/min. at a flow rate of 200 ml/min.

' EXAMPLE 3 In vivo tests The silicone-coated polypropyleneextracorporeal shunt utilized consisted essentially of a cylinder 8 cmhigh and 10 cm in diameter. The cylinder was equipped with screens andinlet and outlet ports for connection via sterile tubing to arterial andvenous circulation; the efferent circuit contained air and clot traps.The priming volume of the shunt was 300 ml. Further details of the shuntare given by Chang et al., Trans. Amer. Soc. Artif. Intern. Organs, 14,163-158 (1968).

The following experiments were carried out in mongrel dogs weighingbetween 20 and 27 kg, under pentobarbital anesthesia. Systemicheparinization (1 mg/kg of heparin sodium by vein and 2 mg/kg into theshunt) was used for the studies on platelets. Arterial platelet countsvaried by no more than i 4 percent over 2-4 hours. After 2 hours, duringwhich control blood samples were drawn, each dog was connected for 2hours to the extracorporeal shunt chamber by its femoral artery andvein. The mean flow rate was ml/min (i SD. 10 ml). For the studies oncreatinine removal, creatinine (45-70 m'g/kg) was infused intravenouslyinto each acutely nephrectomized animal to obtain an arterial bloodcreatinine level in the range of 10 to 30 percent. This level becamesteady within 2 hours after infusion and remained so within i 2.5 mgpercent-for a further 2 hours in control experiments. Two hours afterinfusion, each dog was connected to the shunt chamber with regionalheparinization to prevent clotting. The mean flow rate was also 120ml/min (:SD. 10 ml).

The decrease in arterial creatinine level after two hours ofhemoperfusion with activated charcoal or microencapsulated charcoal wasabout 35 percent. The decrease was most rapid in the first half hour;the rate with microencapsulated charcoal was only slightly lower thanthat obtained with free charcoal. In addition, the pentobarbitalanesthetic was cleared at 84 -50 ml/min.

The effects of 2 hours of hemoperfusion with activated charcoal and thesame activated charcoal microencapsulated with collodion,heparin-complexed collodion and albumin-coated collodion are'tabulatedbelow:

Arterial creatinine Activated charcoal was effective in loweringarterial creatinine, but it caused a serious fall in the arterialplatelet level. Activated charcoal coated with hepatincomplexedcollodion did not alter the platelet level significantly, but it wasmuch less efficient in removing blood creatinine.Collodion-microencapsulated charcoal, prepared to have very thinmembranes, removed creatinine from the blood almost as efficiently asfree activated charcoal, but there was also a serious decrease in theplatelet level. On the other hand, albumin-coated collodionmicrocapsules caused no significant fall in the platelet level, and theywere nearly as efficient as collodion-coated charcoal microcapsules orfree charcoal in lowering blood creatinine.

Further experiments in five dogs confirmed the in vitro findings thaturic acid was also efficiently removed. These experiments also confirmedthat very little urea and essentially no calcium ion, phosphate, plasmaalbumin or other blood protein is removed using the present system. Inthe absence of a suitable absorbent for the removal of urea, thatcompound has been removed using microencapsulated urease in conjunctionwith an absorbent for ammonia such as microencapsulated charcoal.Microencapsulated ion exchange and/or chelating resins have been usedfor selective ion removal.

Plasma hemoglobin measurements indicated that neither free notmicroencapsulated charcoal caused any hemolysis of perfusing blood. Thepresent system requires heparinization but it appears that thealbumincoated microcapsules can be made nonthrombogenic by incorporatinghepatin into the outer albumin layer.

Unlike uncapsulated charcoal, no charcoal powder was found in smears ofeffluent blood from shunts containing microencapsulated charcoal.Histological sections of lungs after two hours of hemoperfusion through300 g of albumin-coated microencapsulated activated charcoal indicatedno emboli in three dogs treated with preparations which has not beenautoclaved. Only four very small charcoal particles were found inprecapillary vessels of the fourth dog treated with autoclavedmicroencapsulated charcoal. With more careful washing of the autoclavedpreparations, no charcoal particles were found in histological sectionson three subsequently treated dogs. Histological sections of liver,spleen, and kidney obtained from the four treated dogs showed noevidence of charcoal embolism.

In comparative series of experiments, four control pentobarbitalanesthetized dogs underwent percutaneous femoral artery catheterization(14 gauge catheter). Seven pentobarbital anesthetized dogs underwentsimilar percutaneous arterial catheterization followed by two hours ofhemoperfusion through 300 g of sterile albumin-coated microencapsulatedactivated charcoal. All animals were followed for more than a month anno adverse effects were observed.

EXAMPLE 4 Clinical trial. I

B. B. is a 50 year old white male with chronic lung disease. The patientcould not be accommodated in either a chronic hemadialysis of rentaltransplantation program and has been maintained by peritoneal dialysis.On the day of clinical trial, his biochemical data were as follows: BUN102 mg percent, creatinine 16.5 percent,uric acid 12.9 mg percent,sodium 143 meg/l, chloride 98 meg/l, potassium 4.4 meg/l, calcium 7.4 mgpercent, and phosphorous 6.4 mg percent.

The procedure'of hemoperfusion was the same as in the in vivoexperiments. The extracorporeal shunt chamber containing 300 g ofalbumin-coated collodion microencapsulated activated charcoal was used.After percutaneous puncture of the left femoral artery (14 gaugecatheter), 3,000 USP units of heparin was injected into the shunt and5,000 USP units intravenously into the patient. Blood from left femoralartery entered the shunt to displace the 350 cc. saline primingsolution. After discarding the 350 cc. priming solution, the effluentflow from the shunt was returned to the patient by the cephalic vein (14gauge catheter). No blood pump was used and a shunt blood flow of 100inl/min was maintained. At the beginning of the hemoperfusion procedure,the patient stated that there was a smell of ether. It was found thatthis came from a trace amount of residual ether present in the collodionmembranes. This smell disappeared shortly. The patient felt wellthroughout the minute procedure. No other side effects were noted.Instead of nausea and vomiting charcoal encountered by some patientstreated with free activated charcoal hemoperfusion, the patient startedto feel very hungry half-way through the procedure and asked repeated yfor food. The patient accepted this procedure so completely thatimmediately after the procedure, he agreed to have repeatedhemoperfusion in the future. The patient was followed for 48 hours withno adverse effects and was discharged from the hospital.

Biochemical data from the hospital laboratory showed that in 60 minutesof hemoperfusion, plasma creatinine fell from the preperfusion level of16.5 to 14.8 mg percent, and uric acid from 12.9 to 9 mg percent.Hematological and biochemical data showed that 90 minutes ofhemoperfusion did not result in any significant adverse effects onplatelets, neither leukocytosis nor leukopenia were noted; and there wasno significant increase in plasma hemoglobin level. The clearance/shuntblood flow ratio was 0.55 after 15 minutes and 0.40 after 60 minutes forcreatinine; and 0.65 after 15 minutes and 0.55 after 60 minutes for uricacid.

In other trials on patients at a blood flow rate of 200 min/min, theclearance for creatinine was 160 ml/min after 15 minutes and ml/minafter two hours. The clearance for uric acid was 170 ml/min after 15minutes and ml/min after2 hours. These values are much higher than thestandard artificial kidneys being used clinically. No adverse effects onplatelets or other formed elements of blood was observed; nor'were thereany embolisms of charcoal'particles.

Other variations in the making and using of double coated microcapsuleswill suggest themselves-to those skilled in the art and my invention isas claimed.

I claim:

l. A microencapsulated detoxicant composition adapted for reaction in anextracorporeal shunt with waste metabolites and toxins found in bloodcomprising a solid detoxicant coated first with a semipermeable polymermembrane having an effective pore size permitting waste metabolites andtoxins to diffuse therethrough and second with a permeable outer layerof a blood compatible protein.

2. A composition according to claim 1 wherein the solid detoxicant ischarcoal.

3. A composition according to claim 2 wherein the semipermeable polymermembrane is collodion.

4. A method for making a microencapsulated detoxicant compositionadapted formation in an extracorporeal shunt with waste metabolites andtoxins found in blood which comprises coating a solid detoxicant with asemipermeable polymer membrane having an effective pore size permittingwaste metabolites and toxins to diffuse therethrough and then coatingwith a permeable outer layer of a blood compatible protein.

2. A composition according to claim 1 wherein the solid detoxicant ischarcoal.
 3. A composition according to claim 2 wherein thesemipermeable polymer membrane is collodion.
 4. A method for making amicroencapsulated detoxicant composition adapted for reaction in anextracorporeal shunt with waste metabolites and toxIns found in bloodwhich comprises coating a solid detoxicant with a semipermeable polymermembrane having an effective pore size permitting waste metabolites andtoxins to diffuse therethrough and then coating with a permeable outerlayer of a blood compatible protein.